Although it may not be environmentally ‘PC’, with declining levels of fish in the sea, and an increasing population, the optimal intake of oily/carnivorous fish is three to five servings a week. The National Institute of Clinical Evidence (NICE) which advises NHS policy, recommends all heart-attack patients eat two to four portions of oily fish (herring, sardines, mackerel, salmon, tuna, and trout) a week.
In Patrick Holford’s 100% Health Survey of 55,000 people, a person’s chances of being in optimal health goes up by a third for those consuming three or more servings of oily fish a week, compared to two a week. A portion is defined as 140g (5oz), which is a small can of fish or a small fillet of fresh fish, from which one should derive at least 7g of omega-3 essential fats over a week. Of course, if you can buy line-caught fish, that is best for the sea and fish stocks.
| Fish Source FSA 2004 |
Omega-3 g/100g | EPA g/100g | Mercury mg/kg | Omega-3/ mercury ratio |
| Canned tuna | 0.37 | 0.23 | 0.19 | 1.95 |
| Trout | 1.15 | 0.25 | 0.06 | 19.17 |
| Herring | 1.31 | 0.90 | 0.04 | 32.75 |
| Fresh tuna | 1.50 | 0.09 | 0.40 | 3.75 |
| Canned/smoked salmon | 1.54 | 0.47 | 0.04 | 38.50 |
| Canned sardines | 1.57 | 0.47 | 0.04 | 39.25 |
| Fresh mackerel | 1.93 | 0.65 | 0.05 | 38.60 |
| Fresh salmon | 2.70 | 0.69 | 0.05 | 54.00 |
| Swordfish | 2? | 0.13 | 1.40 | 1.43? |
| Marlin | 2? | 1.10 | 1.83? |
The omega-3 and mercury content of fish
Have a look at the table above and you will see that the level of omega-3 and EPA in fish varies (Please note that fish has roughly the same amount of EPA and DHA, with EPA converting into DHA, the brain builder, as needed). The amount of omega-3 is a fraction in canned tuna compared to fresh. This is probably because the oil may be squeezed out, and may be sold to the supplement industry, leaving a drier meat disguised as such by putting the tuna in oil. In the US you can buy tuna in its own oil. It tastes completely different and much better. So don’t rely on canned tuna to provide your omega-3 quota, always try to use fresh fish. Another problem with oily fish is the potential for mercury contamination, particularly in very large fish such as tuna. This is particularly relevant for pregnant women, because mercury is a neurotoxin and can induce birth defects. We recommend tuna maximum once a fortnight during pregnancy and once a week or fortnight otherwise. The same advice applies to big carnivorous fish such as marlin or swordfish. The best all-rounders are probably wild salmon and mackerel. The level of omega-3 in farmed salmon is largely going to depend upon what they are fed.
Oily fish possesses other health benefits unrelated to its omega-3 levels, being very high in protein, vitamin E and selenium, so we would always advise eating your three portions a week (just don’t count canned tuna), but we also suggest supplementing as well, especially on those days that you don’t eat fish.
In terms of supplements, which will both tell you how much omega-3 and how much EPA and DHA they contain, you should aim for taking in about 500mg of combined EPA and DHA (add these two amounts on the label together) a day. If you do this, and eat oily fish three times a week, you’re in the right zone.
If you don’t eat fish, supplementing this kind of amount of omega-3 EPA and DHA is essential. If you are vegan and avoid fish oil supplements, then supplement DHA derived from seaweed. You’ll need 250mg of DHA. If pregnant, doubling this is a wise precaution, after all you’d be building two brains. (If you are vegan we’ll email you about your specific fish and egg-free options.)
